L13. Transition State Structures and Properties of Hydrogen Transfer Reactions of Hydrocarbons: Ab Initio Benchmark Calculations

J. A. Litwinowicz, S. Jurisevic, L. Rendak, M. Zalar, and D. W. Ewing

Department of Chemistry, John Carroll University, Cleveland, OH 44118-4581

Michael J. Manka

Department of Chemistry, University of South Florida, Tampa, FL 33620-3651

mjmanka@aol.com or manka@chuma.cas.usf.edu

Ten model hydrogen transfer reactions, involving H atoms of methyl radicals with molecular hydrogen, methane, ethane, ethene, and ethyne were studied using ab initio quantun mechanical methods in order to determine the level of theory at which activation energy barriers are accurately predicted. The calculations employed the following basis sets: 3-21G, DZP, DZP*, pVTZ, and pVTZ+. The quantum mechanical methods used were unrestricted Hartree-Fock theory and second- and fourth-order many-body perturbation theory. Spin contamination of the wave functions was removed using spin projection techniques. Activation energy barriers are predicted to within 2 kcal/mol of experimental values for most reactions studied. Transition state structures and vibrational frequencies were also obtained and compared with other published ab initio results. Using the current ab initio results, transition state theory and correction for tunneling were used to calculate kinetic rate constants which are compared with available experimentally measured results.